Composite implants having integration surfaces composed of a regular repeating pattern

ABSTRACT

A composite interbody spinal implant including a body having a top surface, a bottom surface, opposing lateral sides, and opposing anterior and posterior portions; a first integration plate affixed to the top surface of the body; and an optional second integration plate affixed to the bottom surface of the body. At least a portion of the first integration plate, optional second integration plate, or both has a roughened surface topography including macro features, micro features, and nano features, without sharp teeth that risk damage to bone structures, adapted to grip bone through friction, inhibit migration of the implant, and promote bone growth. Also disclosed are processes of fabricating a roughened surface topography, which may include separate and sequential macro processing, micro processing, and nano processing steps.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/558,390, filed Jul. 26, 2012, which is a continuation-in-part of U.S.patent application Ser. No. 12/151,198, filed on May 5, 2008, and issuedas U.S. Pat. No. 8,262,737, which is a continuation-in-part of U.S.patent application Ser. No. 11/123,359, filed on May 6, 2005, and issuedas U.S. Pat. No. 7,662,186. The contents of all prior applications areincorporated by reference into this document, in their entirety and forall purposes.

TECHNICAL FIELD

The present invention relates generally to composite interbody spinalimplants and methods of making such implants and, more particularly, tofriction-fit composite spinal implants having a roughened integrationsurface with a repeating pattern of predetermined sizes and shapes.

BACKGROUND OF THE INVENTION

In the simplest terms, the spine is a column made of vertebrae anddiscs. The vertebrae provide the support and structure of the spinewhile the spinal discs, located between the vertebrae, act as cushionsor “shock absorbers.” These discs also contribute to the flexibility andmotion of the spinal column. Over time, the discs may become diseased orinfected, may develop deformities such as tears or cracks, or may simplylose structural integrity (e.g., the discs may bulge or flatten).Impaired discs can affect the anatomical functions of the vertebrae, dueto the resultant lack of proper biomechanical support, and are oftenassociated with chronic back pain.

Several surgical techniques have been developed to address spinaldefects, such as disc degeneration and deformity. Spinal fusion hasbecome a recognized surgical procedure for mitigating back pain byrestoring biomechanical and anatomical integrity to the spine. Spinalfusion techniques involve the removal, or partial removal, of at leastone intervertebral disc and preparation of the disc space for receivingan implant by shaping the exposed vertebral endplates. An implant isthen inserted between the opposing endplates.

Spinal fusion procedures can be achieved using a posterior or ananterior approach, for example. Anterior interbody fusion proceduresgenerally have the advantages of reduced operative times and reducedblood loss. Further, anterior procedures do not interfere with theposterior anatomic structure of the lumbar spine. Anterior proceduresalso minimize scarring within the spinal canal while still achievingimproved fusion rates, which is advantageous from a structural andbiomechanical perspective. These generally preferred anterior proceduresare particularly advantageous in providing improved access to the discspace, and thus correspondingly better endplate preparation.

There are a number of problems, however, with traditional spinalimplants including, but not limited to, improper seating of the implant,implant subsidence (defined as sinking or settling) into the softercancellous bone of the vertebral body, poor biomechanical integrity ofthe endplates, damaging critical bone structures during or afterimplantation, and the like. In summary, at least ten, separatechallenges can be identified as inherent in traditional anterior spinalfusion devices. Such challenges include: (1) end-plate preparation; (2)implant difficulty; (3) materials of construction; (4) implantexpulsion; (5) implant subsidence; (6) insufficient room for bone graft;(7) stress shielding; (8) lack of implant incorporation with vertebralbone; (9) limitations on radiographic visualization; and (10) cost ofmanufacture and inventory.

SUMMARY OF THE INVENTION

The present invention provides for composite interbody spinal implantshaving a body and one or two integration plates. The integration platesinclude integration surfaces with fusion and biologically active surfacegeometry, for example, in regular repeating patterns. The composite bodyalso allows for insertion of the implants without damaging critical bonestructures during or after implantation. Various implant body shapes areprovided to allow for implantation through various access paths to thespine through a patient's body.

In one embodiment, the present invention provides a composite interbodyspinal implant comprising: a body having a top surface, a bottomsurface, opposing lateral sides, opposing anterior and posteriorportions, a substantially hollow center, and a single vertical aperture;a first integration plate affixed to the top surface of the body, thefirst integration plate having a top surface, a bottom surface, opposinglateral sides, opposing anterior and posterior portions, and a singlevertical aperture extending from the top surface to the bottom surfaceand aligning with the single vertical aperture of the body, defining atransverse rim. The top surface of the first integration plate has afirst roughened surface topography including macro features, microfeatures, and nano features, without sharp teeth that risk damage tobone structures, adapted to grip bone through friction generated whenthe implant is placed between two vertebrae and to inhibit migration ofthe implant. Optionally, the implant also includes a second integrationplate affixed to the bottom surface of the body, the second integrationplate having a top surface, a bottom surface, opposing lateral sides,opposing anterior and posterior portions, and a single vertical apertureextending from the top surface to the bottom surface and aligning withthe single vertical aperture of the body, defining a transverse rim. Thetop surface of the optional second integration plate has a secondroughened surface topography including macro features, micro features,and nano features, without sharp teeth that risk damage to bonestructures, adapted to grip bone through friction generated when theimplant is placed between two vertebrae and to inhibit migration of theimplant.

The implant body and/or the integration plate(s) may be fabricated froma metal. A preferred metal is titanium. The implant body may befabricated from a non-metallic material, non-limiting examples of whichinclude polyetherether-ketone, hedrocel, ultra-high molecular weightpolyethylene, and combinations thereof. The implant body may befabricated from both a metal and a non-metallic material, including acomposite thereof. For example, a composite implant may be formed withintegration plates made of titanium combined with a polymeric body.

The roughened topography of the integration plate may include repeatingmicro features and nano features of smooth shapes oriented in oppositionto the biologic forces on the implant and to the insertion direction.The macro, micro, and nano features may also partially or substantiallyoverlap, for example, in a predetermined pattern.

In another embodiment of the invention, a composite interbody spinalimplant comprises a body having a top surface, a bottom surface,opposing lateral sides, opposing anterior and posterior portions, asubstantially hollow center, and a single vertical aperture; a firstintegration plate affixed to the top surface of the body and a secondintegration plate affixed to the bottom surface of the body. In otherwords, the body of the implant is sandwiched between the first andsecond integration plates. The first integration plate and the secondintegration plate each have a top surface, a bottom surface, opposinglateral sides, opposing anterior and posterior portions, and a singlevertical aperture extending from the top surface to the bottom surfaceand aligning with the single vertical aperture of the body, defining atransverse rim. The top surface of the first integration plate and thetop surface of the second integration plate each have a roughenedsurface topography including macro features, micro features, and nanofeatures, without sharp teeth that risk damage to bone structures,adapted to grip bone through friction generated when the implant isplaced between two vertebrae and to inhibit migration of the implant.

The present invention also encompasses a process of fabricating aroughened surface topography on at least one surface of the integrationplate(s). The process may include macro processing at least one of thetop surface of the first integration plate and the top surface of thesecond integration plate, micro processing at least one of the topsurface of the first integration plate and the top surface of the secondintegration plate, and nano processing at least one of the top surfaceof the first integration plate and the top surface of the secondintegration plate. The macro processing, the micro processing, and thenano processing are separate and sequential steps. The macro, micro, andnano process may include mechanical or chemical removal of at least aportion of the top surface(s) of the integration plate(s). For example,the nano process may include mild chemical etching, laser or otherdirected energy material removal, abrasion, blasting, or tumbling,followed by cleaning.

BRIEF DESCRIPTION OF THE DRAWING

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following figures:

FIG. 1 shows an exploded view of a generally oval-shaped implant with anintegration plate;

FIG. 2A shows a perspective view of an embodiment of the interbodyspinal implant having a generally oval shape and roughened surfacetopography on the top surface;

FIG. 2B shows a top view of the embodiment of the interbody spinalimplant illustrated in FIG. 2A;

FIG. 3 shows an anterior view of an embodiment of the interbody spinalimplant having two integration plates, which sandwich the body of theimplant;

FIGS. 4A-4C depict a technique to form the macro features of theroughened surface topography on the integration plate in an embodimentof the invention;

FIG. 4D depicts the macro features of the roughened surface topographyon the integration plate in an embodiment of the invention;

FIG. 5A represents macro-, micro-, and nano-scaled features on anintegration plate;

FIG. 5B shows Ra, Rmax, and Sm for a roughened surface topography;

FIG. 6 shows an exploded view of a curved implant with an integrationplate;

FIG. 7 shows an exploded view of a posterior implant with an integrationplate;

FIG. 8 shows an exploded view of a lateral lumbar implant with anintegration plate;

FIG. 9 shows an exploded view of a generally oval-shaped anteriorcervical implant with an integration plate;

FIG. 10 illustrates one set of process steps that can be used to formmacro, micro, or nano processes;

FIG. 11 graphically represents the average amplitude, Ra;

FIG. 12 graphically represents the average peak-to-valley roughness, Rz;

FIG. 13 graphically represents the maximum peak-to-valley height, Rmax;

FIG. 14 graphically represents the total peak-to-valley of wavinessprofile; and

FIG. 15 graphically represents the mean spacing, Sm.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the present invention may be especially suitedfor placement between adjacent human vertebral bodies. The implants ofthe present invention may be used in procedures such as Anterior LumbarInterbody Fusion (ALIF), Posterior Lumbar Interbody Fusion (PLIF),Transforaminal Lumbar Interbody Fusion (TLIF), and cervical fusion.Certain embodiments do not extend beyond the outer dimensions of thevertebral bodies.

The ability to achieve spinal fusion is directly related to theavailable vascular contact area over which fusion is desired, thequality and quantity of the fusion mass, and the stability of theinterbody spinal implant. Interbody spinal implants, as now taught,allow for improved seating over the apophyseal rim of the vertebralbody. Still further, interbody spinal implants, as now taught, betterutilize this vital surface area over which fusion may occur and maybetter bear the considerable biomechanical loads presented through thespinal column with minimal interference with other anatomical orneurological spinal structures. Even further, interbody spinal implants,according to certain aspects of the present invention, allow forimproved visualization of implant seating and fusion assessment.Interbody spinal implants, as now taught, may also facilitateosteointegration (e.g., formation of direct structural and functionalinterface between the artificial implant and living bone or soft tissue)with the surrounding living bone.

It is generally believed that the surface of an implant determines itsultimate ability to integrate into the surrounding living bone. Withoutbeing limited by theory, it is hypothesized that the cumulative effectsof at least implant composition, implant surface energy, and implantsurface roughness play a major role in the biological response to, andosteointegration of, an implant device. Thus, implant fixation maydepend, at least in part, on the stimulation and proliferation of bonemodeling and forming cells, such as osteoclasts and osteoblasts andlike-functioning cells upon the implant surface. Still further, itappears that these cells attach more readily to relatively roughsurfaces rather than smooth surfaces. In this manner, a surface may bebioactive due to its ability to stimulate cellular attachment andosteointegration. The roughened surface topography of the integrationplate(s) described in this document may better promote theosteointegration of certain embodiments of the present invention. Theroughened surface topography of the integration plate(s) may also bettergrip the vertebral endplate surfaces and inhibit implant migration uponplacement and seating.

Composite Implant

The implants of the present invention are composite implants in that theimplant includes at least a body and one or two integration plates,which may be formed from the same or different materials. Theintegration plate(s) comprise an integration surface (e.g., the topsurface), which is adapted to grip bone through friction generated whenthe implant is placed between two vertebrae and to inhibit migration ofthe implant once implanted. The integration surfaces may also have afusion and biologically active surface geometry. In other words, atleast a portion of the top surface of the first integration plate (e.g.,a first integration surface) and optionally a top surface of a secondintegration plate (e.g., a second integration surface) has a roughenedsurface topography including macro features, micro features, and nanofeatures, without sharp teeth that risk damage to bone structures. Theroughened surface topography may include macro features, micro features,and nano features of a regular repeating pattern, which may promotebiological and chemical attachment or fusion with the bone structure.

Certain embodiments of the interbody implant are substantially hollowand have a generally oval-shaped transverse cross-sectional area.Substantially hollow, as used in this document, means at least about 33%of the interior volume of the interbody spinal implant is vacant. Stillfurther, the substantially hollow portion may be filled with cancellousautograft bone, allograft bone, demineralized bone matrix (DBM), poroussynthetic bone graft substitute, bone morphogenic protein (BMP), orcombinations of those materials.

Referring now to the drawing, in which like reference numbers refer tolike elements throughout the various figures that comprise the drawing,FIG. 1 shows an exploded view of a first embodiment of the interbodyspinal implant 1 especially well adapted for use in an ALIF procedure.The composite interbody spinal implant 1 includes a body 2 having a topsurface 10, a bottom surface 20, opposing lateral sides 30, and opposinganterior 40 and posterior 50 portions.

The implant 1 includes a first integration plate 82 affixed to the topsurface 10 of the body 2 and an optional second integration plate 82(shown in FIG. 3) affixed to the bottom surface 20 of the body 2. Thefirst integration plate 82 and optional second integration plate 82 eachhave a top surface 81, a bottom surface 83, opposing lateral sides,opposing anterior portion 41 and posterior portion 51, and a singlevertical aperture 61 extending from the top surface 81 to the bottomsurface 83 and aligning with the single vertical aperture 60 of the body2.

The top surface 81 of the first integration plate 82 and the top surface81 of the optional second integration plate 82 each have a roughenedsurface topography 80 including macro features, micro features, and nanofeatures, without sharp teeth that risk damage to bone structures,adapted to grip bone through friction generated when the implant 1 isplaced between two vertebrae, inhibit migration of the implant 1, andoptionally promote biological and chemical fusion.

The body 2 may be composed of any suitable biocompatible material. In anexemplary embodiment, the body 2 of the implant 1 is formed of aplastic, polymeric, or composite material. For example, suitablepolymers may comprise silicones, polyolefins, polyesters, polyethers,polystyrenes, polyurethanes, acrylates, and co-polymers and mixturesthereof. Certain embodiments of the present invention may be comprisedof a biocompatible, polymeric matrix reinforced with bioactive fillers,fibers, or both. Certain embodiments of the present invention may becomprised of urethane dimethacrylate (DUDMA)/tri-ethylene glycoldimethacrylate (TEDGMA) blended resin and a plurality of fillers andfibers including bioactive fillers and E-glass fibers. In anotherembodiment, the body comprises polyetherether-ketone (PEEK), hedrocel,or ultra-high molecular weight polyethylene (UHMWPE). Hedrocel is acomposite material composed of carbon and an inert metal, such astantalum. UHMWPE, also known as high-modulus polyethylene (HMPE) orhigh-performance polyethylene (HPPE), is a subset of the thermoplasticpolyethylene, with a high molecular weight, usually between 2 and 6million.

The integration plate(s) 82 may also be composed of a suitablebiocompatible material. In an exemplary embodiment, the at least oneintegration plate 82 is formed of metal. The metal may be coated or notcoated. Suitable metals, such as titanium, aluminum, vanadium, tantalum,stainless steel, and alloys thereof, may be selected by one of ordinaryskill in the art. In a preferred embodiment, however, the at least oneintegration plate 82 includes at least one of titanium, aluminum, andvanadium, without any coatings. In a more preferred embodiment, the atleast one integration plate 82 is comprised of titanium or a titaniumalloy. An oxide layer may naturally form on a titanium or titaniumalloy. Titanium and its alloys are generally preferred for certainembodiments of the present invention due to their acceptable, anddesirable, strength and biocompatibility. In this manner, certainembodiments of the present composite interbody spinal implant may haveimproved structural integrity and may better resist fracture duringimplantation by impact.

The body 2 and at least one integration plate 82 are preferablycompatibly shaped, such that the implant 1 having the body 2 andintegration plate(s) 82 joined together may have a generally oval shape,a generally rectangular shape, a generally curved shape, or any othershape described or exemplified in this specification. Thus, for example,the body 2 and the integration plate(s) 82 may be generally oval-shapedin transverse cross-section. The body 2 and the integration plate(s) 82may be generally rectangular-shaped in transverse cross-section. Thebody 2 and the integration plate(s) 82 may be generally curved-shaped intransverse cross-section.

The body 2 and integration plate(s) 82 of the implant 1 may be the samematerial or may be different. In an exemplary embodiment, the body 2 ofthe implant 1 is formed of a polymeric material and the integrationplate(s) 82 are formed of titanium or a titanium alloy. Preferably, thepolymeric body 2 is sandwiched between two integration plates 82 made oftitanium or a titanium alloy. The surfaces of the implant 1, andparticularly, the integration surfaces (e.g., the top surface 81) of theintegration plates 82 are preferably bioactive, which may be achievedfrom the roughened topography discussed below.

Roughened Surface Topography of the Integration Plate

The implant 1 includes a roughened surface topography 80 on at least aportion of each top surface 81 or integration surface of eachintegration plate 82. As used in this document, the integration surfaceof the integration plate 82 is the surface at least partially in contactwith the vertebral or bone structure. In one embodiment of the presentinvention, the roughened surface topography 80 is obtained by combiningseparate macro processing, micro processing, and nano processing steps.The term “macro” typically means relatively large; for example, in thepresent application, dimensions measured in millimeters (mm). The term“micro” typically means one millionth (10⁻⁶); for example, in thepresent application, dimensions measured in microns (μm) whichcorrespond to 10⁻⁶ meters. The term “nano” typically means one billionth(10⁻⁹); for example, in the present application, dimensions measured innanometers (mil) which correspond to 10⁻⁹ meters. FIG. 5A depicts macro,micro, and nano-sized surface features on an integration plate 82.

The interbody implant 1 has a roughened surface topography 80 on theintegration plate(s) 82 with predefined surface features that (a) engagethe vertebral endplates with a friction fit and, following an endplatepreserving surgical technique, (b) attain initial stabilization, and (c)benefit fusion. The composition of the endplate is a thin layer ofnotch-sensitive bone that is easily damaged by features (such as teeth)that protrude sharply from the surface of traditional implants. Avoidingsuch teeth and the attendant risk of damage, the roughened surfacetopography 80 of the integration plate(s) 82 of the implant 1 does nothave teeth or other sharp, potentially damaging structures; rather, theroughened surface topography 80 may have a pattern of repeating featuresof predetermined sizes, smooth shapes, and orientations. By“predetermined” is meant determined beforehand, so that thepredetermined characteristic of the integration plate(s) 82 of theimplant 1 must be determined, i.e., chosen or at least known, before useof the implant 1.

The shapes of the frictional surface protrusions of the roughenedsurface topography 80 are formed using processes and methods commonlyapplied to remove metal during fabrication of implantable devices suchas chemical, electrical, electrochemical, plasma, or laser etching;cutting and removal processes; casting; forging; machining; drilling;grinding; shot peening; abrasive media blasting (such as sand or gritblasting); and combinations of these subtractive processes. Additiveprocesses such as welding, thermal, coatings, sputtering, and opticalmelt additive processes are also suitable. The resulting surfaces eithercan be random in the shape and location of the features or can haverepeating patterns. This flexibility allows for the design andproduction of surfaces that resist motion induced by loading in specificdirections that are beneficial to the installation process and resistthe opposing forces that can be the result of biologic or patientactivities such as standing, bending, or turning or as a result of otheractivities. The shapes of the surface features when overlapping work toincrease the surface contact area but do not result in undercuts thatgenerate a cutting or aggressively abrasive action on the contactingbone surfaces.

These designed surfaces are composed of various sizes of features that,at the microscopic level, interact with the tissues and stimulate theirnatural remodeling and growth. At a larger scale these features performthe function of generating non-stressful friction that, when combinedwith a surgical technique that retains the most rigid cortical bonestructures in the disc space, allow for a friction fit that does notabrade, chip, perforate, or compromise the critical endplate structures.The features may be divided into three size scales: nano, micro, andmacro. The overlapping of the three feature sizes can be achieved usingmanufacturing processes that are completed sequentially and, therefore,do not remove or degrade the previous method.

The first step in the process may be mechanical (e.g., machining thoughconventional processes) or chemical bulk removal, for example, togenerate macro features. The macro features may be of any suitableshape, for example, roughly spherical in shape, without undercuts orprotruding sharp edges. Other shapes are possible, such as ovals,polygons (including rectangles), and the like. These features may be atleast partially overlapped with the next scale (micro) of features usingeither chemical or mechanical methods (e.g., AlO₂ blasting) inpredetermined patterns which also do not result in undercuts orprotruding sharp edges. The third and final process step is completedthrough more mild (less aggressive) etching (e.g., HCl acid etching)that, when completed, generates surface features in both the micro andnano scales over both of the features generated by the two previoussteps. The nano layer dictates the final chemistry of the implantmaterial.

FIG. 10 illustrates one set of process steps that can be used to form anembodiment of the roughened surface topography 80 according to thepresent invention. As illustrated, there is some overlap in theprocesses that can be applied to form each of the three types offeatures (macro, micro, and nano). For example, acid etching can be usedto form the macro features, then the same or a different acid etchingprocess can be used to form the micro features.

(a) Macro Features

The macro features of the roughened surface topography 80 are relativelylarge features (e.g., on the order of millimeters). The macro featuresmay be formed from subtractive techniques (e.g., mechanical or chemicalbulk removal, for example) or additive techniques (e.g., deposition).Preferably, the macro features are formed by subtractive techniques,which remove portions of the top surface 81 of the integration plates 82(e.g., from the base material that was used to form the integrationplate 82). Suitable subtractive techniques may include for example,machining (e.g., machine tools, such as saws, lathes, milling machines,and drill presses, are used with a sharp cutting tool to physicallyremove material to achieve a desired geometry) or masked etching (e.g.,portions of the surface is protected by a “masking” material whichresists etching and an etching substance is applied to unmaskedportions). The patterns may be organized in regular repeating patternsand optionally overlapping each other. In a preferred embodiment, themacro features may be formed in three, sequential steps.

FIG. 4A illustrates the result of the first step in forming the macrofeatures 102. Specifically, a first cut pattern 103 of the macrofeatures is formed in a surface (e.g., the top surface 81) of theintegration plate 82. The “cut 1” features of the first cut pattern 103may cover about 20% of the total area of the surface, for example,leaving about 80% of the original surface 104 remaining. The range ofthese percentages may be about ±20%, preferably ±10%, and morepreferably about ±5%. The “cut 1” features of the first cut pattern 103do not have any undercuts. In one embodiment, these “cut 1” featureshave the smallest diameter and greatest depth of the macro features thatare formed during the sequential steps.

FIG. 4B illustrates the result of the second step in forming the macrofeatures. Specifically, a second cut pattern 105 of the macro featuresis formed in the surface of the integration plate 82. Together, the “cut1” features of the first cut pattern 103 and the “cut 2” features of thesecond cut pattern 105 may cover about 85% of the total area of thesurface, for example, leaving about 15% of the original surface 104remaining. The range of these percentages may be about ±10% andpreferably ±5%. In an embodiment of the invention, these “cut 2”features have both a diameter and a depth between those of the “cut 1”and “cut 3” features of the macro features that are formed during thefirst and third steps of the process of forming the macro features ofthe roughened surface topography 80.

FIG. 4C illustrates the result of the third and final step in formingthe macro features. Specifically, a third cut pattern 107 of the macrofeatures may be formed in the surface of the integration plate 82.Together, the “cut 1” features of the first cut pattern 103, the “cut 2”features of the second cut pattern 105, and the “cut 3” features of thethird cut pattern 107 cover about 95% of the total area of the surface,for example, leaving about 5% of the original surface 104 remaining. Therange of these percentages may be about ±1%. In an embodiment of theinvention, these “cut 3” features may have the largest diameter andleast depth of the macro features that are formed during the sequentialprocess steps.

FIG. 4D also depicts the roughened surface topography 80 on the implant1 following completion of the three, sequential processing steps. Asshown, the finished macro features comprise multiple patterns of thethree, overlapping cuts: the first cut pattern 103, the second cutpattern 105, and the third cut pattern 107.

(b) Micro Features

After the macro features 102 are formed in the integration plate 82,additional process steps may be sequentially applied to the integrationplate 82 of the implant 1, in turn, to form the micro surface features(e.g., on the order of micrometers) of the roughened surface topography80. The micro features may also be formed from subtractive techniques(e.g., mechanical or chemical bulk removal, for example) or additivetechniques (e.g., deposition). Preferably, the micro features are alsoformed by subtractive techniques.

In an exemplary embodiment, the micro features are removed by masked orunmasked etching, such as acid etching. For example, portions of thesurface of the integration plate 82, including portions of the surfaceexposed by the macro step(s) described above, may be exposed to achemical etching. In an exemplary embodiment, the micro process includesan acid etching, with a strong acid, such as hydrochloric acid (HCl),hydroiodic acid (HI), hydrobromic acid (HBr), hydrofluoric (HF),perchloric acid (HClO₄), nitric acid (HNO₃), sulfuric acid (H₂SO₄), andthe like. The etching process may be repeated a number of times asnecessitated by the amount and nature of the irregularities required forany particular application. Control of the strength of the etchantmaterial, the temperature at which the etching process takes place, andthe time allotted for the etching process allows fine control over theresulting surface produced by the process. The number of repetitions ofthe etching process can also be used to control the surface features.For example, the roughened surface topography 80 may be obtained via therepetitive masking and chemical or electrochemical milling processesdescribed in U.S. Pat. No. 5,258,098; No. 5,507,815; No. 5,922,029; andNo. 6,193,762, the contents of which are incorporated by reference intothis document, in their entirety, and for all purposes.

By way of example, an etchant mixture of at least one of nitric acid andhydrofluoric acid may be repeatedly applied to a titanium surface toproduce an average etch depth of about 0.53 mm. In another example,chemical modification of a titanium integration plate 82 can be achievedusing at least one of hydrofluoric acid, hydrochloric acid, and sulfuricacid. In a dual acid etching process, for example, the first exposure isto hydrofluoric acid and the second is to a hydrochloric acid andsulfuric acid mixture. Chemical acid etching alone may enhanceosteointegration without adding particulate matter (e.g.,hydroxyapatite) or embedding surface contaminants (e.g., gritparticles).

The micro features may also be created by abrasive or grit blasting, forexample, by applying a stream of abrasive material (such as alumina,sand, and the like) to the surface of the integration plate 82. In anexemplary embodiment, the micro features are created, at leastpartially, with an aqueous hydrochloric acid etching step and at leastpartially with an AlO₂ blasting step. Patterns may be organized inregular repeating patterns and optionally overlapping each other. Afterthe micro features are formed, it is possible that less than about 3% ofthe original surface 104 of the integration plate 82 remains. The rangeof that percentage may be about ±1%.

(c) Nano Features

After the macro features and micro features are formed in theintegration plate 82, additional process steps may be sequentiallyapplied to the integration plate 82 of the implant 1, in turn, to formthe nano surface features (e.g., on the order of nanometers) of theroughened surface topography 80. The nano features may also be formedfrom subtractive techniques (e.g., mechanical or chemical bulk removal,for example) or additive techniques (e.g., deposition). Preferably, thenano features are also formed by subtractive techniques.

In an exemplary embodiment, the nano features are removed by masked orunmasked etching. For example, portions of the surface of theintegration plate 82, including portions of the surface exposed by themacro and micro steps described above, may be exposed to a chemicaletching. In an exemplary embodiment, the nano process also includes anacid etching, with a strong or weak acid, such as hydrochloric acid(HCl), hydroiodic acid (HI), hydrobromic acid (HBr), hydrofluoric (HF),perchloric acid (HClO₄), nitric acid (HNO₃), sulfuric acid (H₂SO₄), andthe like. The acid etching process for the nano step is preferably lessaggressive than the acid etching process in the micro step. In otherwords, a less acidic, mild, or more diluted acid may be selected. In anexemplary embodiment, the nano features are created, at least partially,with an aqueous hydrochloric acid etching step.

As an example, the nano features may be formed by preparing an acidsolution comprising hydrochloric acid, water, and titanium; applying theacid solution to the top surface of the integration plate 82; removingthe acid solution by rinsing with water; and heating and subsequentlycooling the integration plate 82.

The acid solution may be prepared using any suitable techniques known inthe art. For example, the acid solution may be prepared by combininghydrochloric acid and water, simultaneously or sequentially. The aqueoushydrochloric acid solution may optionally be heated, for example, to atemperature of about 150-250° F., preferably about 200-210° F., and mostpreferably about 205° F. The titanium may be seeded (e.g., added) in theaqueous hydrochloric acid solution or may already be present fromtitanium previously removed from at least one surface of the implant,for example, in a continuous manufacturing process. The solution mayoptionally be cooled. The acid solution may comprise a concentration of20-40% hydrochloric acid, preferably about 25-31% hydrochloric acid, andmore preferably about 28% hydrochloric acid, based on the weight percentof the solution.

The acid solution may be applied to the top surface 81 of theintegration plate 82 using any suitable mechanism or techniques known inthe art, for example, immersion, spraying, brushing, and the like. In anexemplary embodiment, the acid solution is applied to the integrationplate 82 by immersing the entire integration plate 82 in the solution.It is also contemplated that the integration plate 82 may be immersed inthe acid solution alone or in combination with the assembled implant 1(i.e., including the body 2). If desired, certain areas of theintegration plate 82 or the implant 1 may be masked in patterns or toprotect certain portions of the implant 1. The acid solution may beheated when it is applied to the integration plate 82. For example, thesolution may be heated to a temperature of about 150-250° F., preferablyabout 200-210° F., and most preferably about 205° F. The solution mayalso be applied for any suitable period of time. For example, thesolution may be applied to the integration plate 82 for a period of timeof about 5-30 minutes, preferably about 15-25 minutes, and morepreferably about 20 minutes.

After the acid solution is applied, the acid solution may be removed,for example, by rinsing with water (e.g., deionized water). Theintegration plate 82 or entire implant 1 may be subsequently dried. Theintegration plate 82 may be dried using any suitable mechanism ortechniques known in the art, for example, by heating in an oven (e.g., adry oven). The integration plate may be heated to a temperature of about110-130° F., preferably about 120-125° F., and most preferably about122.5° F. The integration plate may be heated for any suitable period oftime, for example about 30-50 minutes, preferably about 35-45 minutes,and more preferably about 40 minutes. After heating, the integrationplate 82 may be cooled to room temperature, for example.

It is contemplated that the nano features may also be created by theabrasive or grit blasting, for example, described for the microprocessing step. Patterns may be organized in regular repeating patternsand optionally overlapping each other. The nano features may also beachieved by tumble finishing (e.g., tumbling) the part or the implant 1.Suitable equipment and techniques can be selected by one of ordinaryskill in the art. For example, a barrel may be filled with the parts orimplants 1 and the barrel is then rotated. Thus, the part or implants 1may be tumbled against themselves or with steel balls, shot, rounded-endpins, ballcones, or the like. The tumbling process may be wet (e.g.,with a lubricant) or dry. After the nano features are formed, it ispossible that less than about 1% of the original surface 104 of theintegration plate 82 remains. For example, after the nano features areformed, the roughened surface topography 80 may cover substantially allof the top surface 81 of the integration plate 82.

As should be readily apparent to a skilled artisan, the process stepsdescribed in this document can be adjusted to create a mixture ofdepths, diameters, feature sizes, and other geometries suitable for aparticular implant application. The orientation of the pattern offeatures can also be adjusted. Such flexibility is desirable, especiallybecause the ultimate pattern of the roughened surface topography 80 ofthe integration plate 82 of the implant 1 should be oriented inopposition to the biologic forces on the implant 1 and to the insertiondirection. In one particular embodiment, for example, the pattern of theroughened surface topography 80 may be modeled after an S-shaped tiretread.

Roughness Parameters

Several separate parameters can be used to characterize the roughness ofan implant surface. Among those parameters are the average amplitude,Ra; the maximum peak-to-valley height, Rmax; and the mean spacing, Sm.Each of these three parameters, and others, are explained in detailbelow. Meanwhile, FIG. 5B illustrates all three parameters, namely, Ra,Rmax, and Sm, for the macro features 102 of the integration plate 82.Surface roughness may be measured using a laser profilometer or otherstandard instrumentation.

In addition to the parameters Ra, Rmax, and Sm mentioned above, at leasttwo other parameters can be used to characterize the roughness of animplant surface. In summary, the five parameters are: (1) averageamplitude, Ra; (2) average peak-to-valley roughness, Rz; (3) maximumpeak-to-valley height, Rmax; (4) total peak-to-valley of wavinessprofile, Wt; and (5) mean spacing, Sm. Each parameter is explained indetail as follows.

1. Average Amplitude Ra

In practice, “Ra” is the most commonly used roughness parameter. It isthe arithmetic average height. Mathematically, Ra is computed as theaverage distance between each roughness profile point and the mean line.In FIG. 11, the average amplitude is the average length of the arrows.

In mathematical terms, this process can be represented as

${Ra} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}\;{y_{i}}}}$

2. Average Peak-to-Valley Roughness Rz

The average peak-to-valley roughness, Rz, is defined by the ISO and ASME1995 and later. Rz is based on one peak and one valley per samplinglength. The RzDIN value is based on the determination of thepeak-to-valley distance in each sampling length. These individualpeak-to-valley distances are averaged, resulting in the RzDIN value, asillustrated in FIG. 12.

3. Maximum Peak-to-Valley Height Rmax

The maximum peak-to-valley height, Rmax, is the maximum peak-to-valleydistance in a single sampling length—as illustrated in FIG. 13.

4. Total Peak-to-Valley of Waviness Profile Wt

The total peak-to-valley of waviness profile (over the entire assessmentlength) is illustrated in FIG. 14.

5. Mean Spacing Sm

The mean spacing, Sm, is the average spacing between positive mean linecrossings. The distance between each positive (upward) mean linecrossing is determined and the average value is calculated, asillustrated in FIG. 15.

The parameters Sm, Rmax, and Ra can be used define the surface roughnessfollowing formation of each of the three types of features macro, micro,and nano. Such data are provided in Table 2 below.

TABLE 2 EXAMPLE DATA BY PROCESS STEP Size (Sm) Depth (Rmax) Roughness(Ra) Surface Feature Size and Roughness (Metric): Macro (μm) Max. 2,000500 200 Min. 400 40 20 Avg. 1,200 270 110 Surface Feature Size andRoughness (Metric): Micro (μm) Max. 400 40 20 Min. 20 2 1 Avg. 210 115.5 Surface Feature Size and Roughness (Metric): Nano (μm) Max. 20 2 1Min. 0.5 0.2 0.01 Avg. 10.25 1.1 0.505

From the data in Table 2, the following preferred ranges (allmeasurements in microns) can be derived for the macro features for eachof the three parameters. The mean spacing, Sm, is between about400-2,000, with a range of 750-1,750 preferred and a range of1,000-1,500 most preferred. The maximum peak-to-valley height, Rmax, isbetween about 40-500, with a range of 150-400 preferred and a range of250-300 most preferred. The average amplitude, Ra, is between about20-200, with a range of 50-150 preferred and a range of 100-125 mostpreferred.

The following preferred ranges (all measurements in microns) can bederived for the micro features for each of the three parameters. Themean spacing, Sm, is between about 20-400, with a range of 100-300preferred and a range of 200-250 most preferred. The maximumpeak-to-valley height, Rmax, is between about 2-40, with a range of 2-20preferred and a range of 9-13 most preferred. The average amplitude, Ra,is between about 1-20, with a range of 2-15 preferred and a range of4-10 most preferred.

The following preferred ranges (all measurements in microns) can bederived for the nano features for each of the three parameters. The meanspacing, Sm, is between about 0.5-20, with a range of 1-15 preferred anda range of 5-12 most preferred. The maximum peak-to-valley height, Rmax,is between about 0.2-2, with a range of 0.2-1.8 preferred and a range of0.3-1.3 most preferred. The average amplitude, Ra, is between about0.01-1, with a range of 0.02-0.8 preferred and a range of 0.03-0.6 mostpreferred.

Integration Plate and Attachment

The integration plate, shown in the drawing as component 82 (FIGS. 1, 3,4A-4C, and 5), 182 (FIG. 7), 182 a (FIG. 6), 382 (FIG. 8), and 282 (FIG.9), respectively, includes the roughened surface topography 80, 180, 180a, 280, and 380, and is connectable to either or both of the top surface10, 110, 110 a, 210, and 310 or bottom surface 20, 120, 120 a, 220, and320. The integration plate 82, 182, 182 a, 282, and 382 includes a topsurface 81, 181, 181 a, 281, and 381; a bottom surface 83, 183, 183 a,283, and 383; an anterior portion 41, 141, 141 a, 241, and 341; aposterior portion 51, 151, 151 a, 251, and 351; and at least onevertical aperture 61, 161, 161 a, 261, and 361. The anterior portion 41,141, 141 a, 241, and 341 preferably aligns with the anterior portion 40,140, 140 a, 240, and 340 of the main body of the implant 1, 101, 101 a,201, and 301, respectively, and the posterior portion 51, 151, 151 a,251, and 351 aligns with the posterior portion 50, 150, 150 a, 250, and350 of the main body of the implant 1, 101, 101 a, 201, and 301,respectively. The vertical aperture 61, 161, 161 a, 261, and 361preferably aligns with the vertical aperture 60, 160, 160 a, 260, and360 of the main body of the implant 1, 101, 101 a, 201, and 301,respectively. Thus, the integration plate vertical aperture 61, 161, 161a, 261, and 361 and the body vertical aperture 60, 160, 160 a, 260, and360 preferably comprise substantially the same shape.

The integration plate 82, 182, 182 a, 282, and 382 may be attached oraffixed to the main body of the implant 1, 101, 101 a, 201, and 301using any suitable mechanisms known in the art. For example, the bottomsurface 83, 183, 183 a, 283, and 383 of the integration plate 82, 182,182 a, 282, and 382 may comprise a reciprocal connector structure, suchas a plurality of posts 84, 184, 184 a, 284, and 384 that align with andinsert into a corresponding connector structure such as a plurality ofholes 12, 112, 112 a, 212, and 312 on the top surface 10, 110, 110 a,210, and 310 and/or bottom surface 20, 120, 120 a, 220, and 320 of themain body of the implant 1, 101, 101 a, 201, and 301, respectively, andthus facilitate the connection between the integration plate 82, 182,182 a, 282, and 382 and the main body of the implant 1, 101, 101 a, 201,and 301. Thus, integration plates 82, 182, 182 a, 282, and 382 withdifferent sizes, shapes, or features may be used in connection with theimplant 1, 101, 101 a, 201, and 301, for example, to accommodateattributes of the spine of the patient to which the implant 1, 101, 101a, 201, and 301 is to be implanted. Among these different sizes, shapes,and features are lordotic angles; anti-expulsion edges 8, 108, 108 a,208, and 308; and anti-expulsion angles as described throughout thisspecification.

The implant 1, 101, 101 a, 201, and 301 is configured to receive theintegration plate 82, 182, 182 a, 282, and 382, respectively. Thus, forexample, the top surface 10, 110, 110 a, 210, and 310 and/or bottomsurface 20, 120, 120 a, 220, and 320 of the implant 1, 101, 101 a, 201,and 301 may be optionally recessed, and comprise a plurality of holes12, 112, 112 a, 212, and 312 that mate with the plurality of posts 84,184, 184 a, 284, and 384 on the bottom surface 83, 183, 183 a, 283, and383 of the integration plate 82, 182, 182 a, 282, and 382. Thus, theplurality of posts 84, 184, 184 a, 284, and 384 are inserted into theplurality of holes 12, 112, 112 a, 212, and 312.

FIG. 1 shows that the top surface 10 is recessed and comprises aplurality of holes 12, but the recessed bottom surface 20 and its holes12 are not shown. FIG. 6 shows that the top surface 110 a is recessedand comprises a plurality of holes 112 a, but the recessed bottomsurface 120 a and its holes 112 a are not shown. FIG. 7 shows that thetop surface 110 is recessed and comprises a plurality of holes 112, butthe recessed bottom surface 120 and its holes 112 are not shown. FIG. 8shows that the top surface 310 is recessed and comprises a plurality ofholes 312, but the recessed bottom surface 320 and its holes 312 are notshown. FIG. 9 shows that the top surface 210 is recessed and comprises aplurality of holes 212, but the recessed bottom surface 220 and itsholes 212 are not shown. The recess may be at a depth D, and the recessdepth D preferably is uniform throughout the top surface 10, 110, 110 a,210, and 310 and/or bottom surface 20, 120, 120 a, 220, and 320.

The recess depth D preferably corresponds to a thickness T of theintegration plate 82, 182, 182 a, 282, and 382. Thus, in some aspects,the depth D and thickness T are the same so that once the integrationplate 82, 182, 182 a, 282, and 382 and body of the implant 1, 101, 101a, 201, and 301, respectively, are placed together, the top surface 10,110, 110 a, 210, and 310 and/or bottom surface 20, 120, 120 a, 220, and320 of the implant 1, 101, 101 a, 201, and 301 is substantially even, atleast at the seam/junction between the integration plate 82, 182, 182 a,282, and 382 and the top surface 10, 110, 110 a, 210, and 310 or bottomsurface 20, 210, 120 a, 220, and 320. In some embodiments, the posteriorportion 51, 151, 151 a, 251, and 351 and the anterior portion 41, 141,141 a, 241, and 341 of the integration plate 82, 182, 182 a, 282, and382 have different thicknesses such that the anterior portion 41, 141,141 a, 241, and 341 has a greater thickness than the thickness of theposterior portion 51, 151, 151 a, 251, and 351.

The recess depth D and the thickness T may each independently be fromabout 0.1 mm to about 10 mm. In preferred aspects, the recess depth Dand the thickness T may each independently be from about 1 mm to about 5mm. Thus, for example, the recess depth D and the thickness T may beselected from about 0.1 mm, about 0.25 mm, about 0.5 mm, about 0.75 mm,about 1 mm, about 1.25 mm, about 1.5 mm, about 1.75 mm, about 2 mm,about 2.25 mm, about 2.5 mm, about 2.75 mm, about 3 mm, about 3.25 mm,about 3.5 mm, about 3.75 mm, about 4 mm, about 4.25 mm, about 4.5 mm,about 4.75 mm, about 5 mm, 5.5 mm, about 6 mm, about 6.5 mm, about 7 mm,about 75 mm, or about 8 mm.

Recessing the top surface 10, 110, 110 a, 210, and 310 or bottom surface20, 120, 120 a, 220, and 320 exposes a ridge 11, 111, 111 a, 211, and311 against which the anterior portion 41, 141, 141 a, 241, and 341,posterior portion 51, 151, 151 a, 251, and 251, or lateral side of theintegration plate 82, 182, 182 a, 282, and 382 may be seated whenbrought together with the implant 1, 101, 101 a, 201, and 301.

The integration plate 82, 182, 182 a, 282, and 382 may be used with animplant suitable for ALIF (e.g., implant 1, integration plate 82), PLIF(e.g., implant 101, integration plate 182), or TLIF fusion (e.g.,implant 101 a, integration plate 182 a); may be used with an implantsuitable for cervical fusion (e.g., implant 201, integration plate 282);and may be used with an implant suitable for lateral lumbar insertion(e.g., implant 301, integration plate 382).

The reciprocal connector such as the post 84, 184, 184 a, 284, and 384preferably is secured within the connector of the body such as the hole12, 112, 112 a, 212, and 312 to mediate the connection between theintegration plate 82, 182, 182 a, 282, and 382 and the implant 1, 101,101 a, 201, and 301. The connection should be capable of withstandingsignificant loads and shear forces when implanted in the spine of thepatient. The connection between the post 84, 184, 184 a, 284, and 384and the hole 12, 112, 112 a, 212, and 312 may comprise a friction fit.In some aspects, the reciprocal connector such as the post 84, 184, 184a, 284, and 384 and the connector of the body such as the hole 12, 112,112 a, 212, and 312 have additional compatible structures and featuresto further strengthen the connection between the integration plate 82,182, 182 a, 282, and 382 and the implant 1, 101, 101 a, 201, and 301.

The structures and features may be on either or both of the integrationplate 82, 182, 182 a, 282, and 382 and the main body 2 of the implant 1,101, 101 a, 201, and 301. In general, the structures include fasteners,compatibly shaped joints, compatibly shaped undercuts, and/or othersuitable connectors having different shapes, sizes, and configurations.For example, a fastener may include a pin, screw, bolt, rod, anchor,snap, clasp, clip, clamp, or rivet. In some aspects, an adhesive may beused to further strengthen any of the integration plate 82, 182, 182 a,282, and 382 and implant 1, 101, 101 a, 201, and 301 connectionsdescribed in this specification. An adhesive may comprise cement, glue,polymer, epoxy, solder, weld, or other suitable binding materials.

The integration plate 82, 182, 182 a, 282, and 382 may comprise one ormore reciprocal connectors (not shown), such as one or more posts, eachhaving a bore, extending through a horizontal plane. The post may beinserted into a connector such as a hole through the implant 1, 101, 101a, 201, and 301. A fastener (not shown), such as a pin, may be insertedthrough the bore thereby preventing the post from being disengaged fromthe hole. In some aspects, the pin may be threaded through a second borethat passes through the walls of the implant itself, although it ispreferable that the implant 1, 101, 101 a, 201, and 301 does not includea second bore through its walls and that the bore is accessible from thespace inside of the implant 1, 101, 101 a, 201, and 301. Alternatively,the integration plate 82, 182, 182 a, 282, and 382 may comprise aplurality of bores (not shown) present on and having an openingaccessible from the bottom of the integration plate 82, 182, 182 a, 282,and 382. The bores may mate with a plurality of fasteners, which maycomprise rods integral with or otherwise attached to the top surface orbottom surface of the implant 1, 101, 101 a, 201, and 301. For example,the rods may be molded as upward-facing extensions or snap-fit into thebores. In some aspects, for example, where the body 2 of the implant 1,101, 101 a, 201, and 301 is comprised of a plastic or polymericmaterial, the hole 12, 112, 112 a, 212, and 312 may not be present, andthe screw or bolt (not shown) may be screwed directly into the plasticor polymeric material, with the screw threads tightly gripping theplastic or polymeric material to form the connection.

It is also contemplated that the bottom surface 83, 183, 183 a, 283, and383 of the integration plate 82, 182, 182 a, 282, and 382 may compriseundercuts (not shown) in shapes that form a tight junction withcompatible shapes on the implant 1, 101, 101 a, 201, and 301. Forexample, the bottom surface 83, 183, 183 a, 283, and 383 may comprise adovetail joint, bevel, or taper that fits with a counterpart dovetailjoint, bevel, or taper on the implant 1, 101, 101 a, 201, and 301 body2.

An adhesive (not shown) may directly join the integration plate 82, 182,182 a, 282, and 382 and body 2 of the implant 1, 101, 101 a, 201, and301 together, with or without other connecting features. For example,the adhesive may be applied to the bottom surface 83, 183, 183 a, 283,and 383 of the integration plate 82, 182, 182 a, 282, and 382 or 10,110, 110 a, 210, and 310 or bottom surface 20, 120, 120 a, 220, and 320,or both of the body 2 of the implant 1, 101, 101 a, 201, and 301.

The foregoing describes various non-limiting examples of how the one ortwo integration plates 82, 182, 182 a, 282, and 382 may be joinedtogether with the implant 1, 101, 101 a, 201, and 301.

Other Implant Features

The implant 1 may comprise some or all of the following implantfeatures, for example. In some aspects, the composite interbody spinalimplant 1 is substantially hollow and has a generally oval-shapedtransverse cross-sectional area with smooth, rounded, or both smooth androunded lateral sides 30 and posterior-lateral corners. The implant 1includes at least one vertical aperture 60 that extends the entireheight of the implant body. The vertical aperture (a) extends from thetop surface to the bottom surface, (b) has a size and shapepredetermined to maximize the surface area of the top surface and thebottom surface available proximate the anterior and posterior portionswhile maximizing both radiographic visualization and access to thesubstantially hollow center, and (c) optionally defines a transverserim. The vertical aperture 60 may further define a transverse rim 100having a greater posterior portion thickness 55 than an anterior portionthickness 45.

In at least one embodiment, the opposing lateral sides 30 and theanterior portion 40 have a rim thickness 45 of about 5 mm, while theposterior portion 50 has a rim thickness 55 of about 7 mm. Thus, the rimposterior portion thickness 55 may allow for better stress sharingbetween the implant 1 and the adjacent vertebral endplates and helps tocompensate for the weaker posterior endplate bone. In some aspects, thetransverse rim 100 has a generally large surface area and contacts thevertebral endplate. The transverse rim 100 may act to better distributecontact stresses upon the implant 1, and hence minimize the risk ofsubsidence while maximizing contact with the apophyseal supportive bone.It is also possible for the transverse rim 100 to have a substantiallyconstant thickness (e.g., for the anterior portion thickness 45 to besubstantially the same as the posterior portion thickness 55) or for theposterior portion 50 to have a rim thickness 55 less than that of theopposing lateral sides 30 and the anterior portion 40.

The implant 1 may be shaped to reduce the risk of subsidence, andimprove stability, by maximizing contact with the apophyseal rim ofvertebral endplates. Embodiments may be provided in a variety ofanatomical footprints having a medial-lateral width ranging from about32 mm to about 44 mm. An interbody spinal implant 1 generally does notrequire extensive supplemental or obstructive implant instrumentation tomaintain the prepared disc space during implantation. Thus, theinterbody spinal implant 1 and associated implantation methods allow forlarger-sized implants as compared with other size-limited interbodyspinal implants known in the art. This advantage allows for greatermedial-lateral width and correspondingly greater contact with theapophyseal rim.

As illustrated in FIG. 2A, the implant 1 has an opening 90 in theanterior portion 40. In one embodiment, the posterior portion 50 mayhave a similarly shaped opening 90 (not shown). In some aspects, onlythe anterior portion 40 has the opening 90 while the posterior portion50 has an alternative opening 92 (which may have a size and shapedifferent from the opening 90).

The opening 90, 290, and 390 has a number of functions. One function isto facilitate manipulation of the implant 1, 201, and 301 by thecaretaker. Thus, the caretaker may insert a surgical tool into theopening 90, 290, and 390 and, through the engagement between thesurgical tool and the opening 90, 290, and 390, manipulate the implant1, 201, and 301. The opening 90, 290, and 390 may be threaded to enhancethe engagement. A suitable surgical tool, such as a distractor (notshown), may be selected by one of ordinary skill in the art.

As best shown in FIG. 6 and FIG. 7, the anterior portion 140, 140 a mayhave a tapered nose 142, 142 a to facilitate insertion of the implant101.

The implant 1 may further include at least one transverse aperture 70that extends the entire transverse length of the implant body. The atleast one transverse aperture 70 may provide improved visibility of theimplant 1 during surgical procedures to ensure proper implant placementand seating, and may also improve post-operative assessment of implantfusion. The transverse aperture 70 may be broken into two, separatesections by an intermediate wall. Suitable shapes and dimensions for thetransverse aperture 70 may be selected by one of ordinary skill in theart. In particular, all edges of the transverse aperture 70 may berounded, smooth, or both. The intermediate wall may be made of the samematerial as the remainder of the body 2 of the implant 1 (e.g.,plastic), or it may be made of another material (e.g., metal). Theintermediate wall may offer one or more of several advantages, includingreinforcement of the implant 1 and improved bone graft containment.

The implant 1 may be provided with a solid rear wall (not shown). Therear wall may extend the entire width of the implant body and nearly theentire height of the implant body. Thus, the rear wall can essentiallyclose the anterior portion 40 of the implant 1. The rear wall may offerone or more of several advantages, including reinforcement of theimplant 1 and improved bone graft containment. In the cervicalapplication, it may be important to prevent bone graft material fromentering the spinal canal.

The implant 1 may also have a lordotic angle to facilitate alignment.One lateral side 30 is preferably generally greater in height than theopposing lateral side 30. Therefore, the implant 1 may better compensatefor the generally less supportive bone found in certain regions of thevertebral endplate. As much as seven degrees of lordosis (or more) maybe built into the implant 1 to help restore cervical balance.

To enhance movement resistance and provide additional stability underspinal loads in the body, the implant 1, 101, 101 a, 201, and 301 maycomprise one or more anti-expulsion edges 8, 108, 108 a, 208, and 308that tend to “dig” into the end-plates slightly and help to resistexpulsion. The anti-expulsion edges 8, 108, 108 a, 208, and 308 may bepresent on the top surface 81 of the integration plate 82 affixed to thetop surface 10, 110, 110 a, 210, and 310; the bottom surface 20, 120,120 a, 220, and 320; or both surfaces of the implant 1, 101, 101 a, 201,and 301. Alternatively, the anti-expulsion edges 8, 108, 108 a, 208, and308 may be present on the top surface 10, 110, 110 a, 210, and 310; thebottom surface 20, 120, 120 a, 220, and 320; or both surfaces of thebody of the implant 1, 101, 101 a, 201, and 301.

By way of example, FIG. 1 shows an anti-expulsion edge 8 on the topsurface 81 of the integration plate 82 and the bottom surface 20 of theanterior face 40 of the implant 1. Each anti-expulsion edge 8 mayprotrude above the plane of the top surface 81 of the integration plate82 and bottom surface 20, with the amount of protrusion increasingtoward the anterior face 40 and the highest protrusion height P at theanterior-most edge of the top surface 81 of the integration plate 82 orbottom surface 20.

An anti-expulsion edge 8, 108, 108 a, 208, and 308 may be orientedtoward the anterior portion 40, 140, 140 a, 240, and 340, or theposterior portion 50, 150, 150 a, 250, and 350, or either of theopposing lateral sides 30, 130, 130 a, 230, and 330. The orientation ofthe anti-expulsion edge 8, 108, 108 a, 208, and 308 may depend on theintended orientation of the implant 1, 101, 101 a, 201, and 301 when ithas been implanted between vertebrae in the patient.

Example Surgical Methods

The following examples of surgical methods are included to more clearlydemonstrate the overall nature of the invention. These examples areexemplary, not restrictive, of the invention.

Certain embodiments of the invention are particularly suited for useduring interbody spinal implant procedures currently known in the art.For example, the disc space may be accessed using a standard mini openretroperitoneal laparotomy approach. The center of the disc space islocated by AP fluoroscopy taking care to make sure the pedicles areequidistant from the spinous process. The disc space is then incised bymaking a window in the annulus for insertion of certain embodiments ofthe spinal implant 1 (a 32 or 36 mm window in the annulus is typicallysuitable for insertion). The process according to the inventionminimizes, if it does not eliminate, the cutting of bone. The endplatesare cleaned of all cartilage with a curette, however, and asize-specific rasp (or broach) may then be used.

Use of a rasp preferably substantially minimizes or eliminates removalof bone, thus substantially minimizing or eliminating impact to thenatural anatomical arch, or concavity, of the vertebral endplate whilepreserving much of the apophyseal rim. Preservation of the anatomicalconcavity is particularly advantageous in maintaining biomechanicalintegrity of the spine. For example, in a healthy spine, the transfer ofcompressive loads from the vertebrae to the spinal disc is achieved viahoop stresses acting upon the natural arch of the endplate. Thedistribution of forces, and resultant hoop stress, along the naturalarch allows the relatively thin shell of subchondral bone to transferlarge amounts of load.

During traditional fusion procedures, the vertebral endplate naturalarch may be significantly removed due to excessive surface preparationfor implant placement and seating. This is especially common where theimplant is to be seated near the center of the vertebral endplate or theimplant is of relatively small medial-lateral width. Breaching thevertebral endplate natural arch disrupts the biomechanical integrity ofthe vertebral endplate such that shear stress, rather than hoop stress,acts upon the endplate surface. This redistribution of stresses mayresult in subsidence of the implant into the vertebral body.

Preferred embodiments of the surgical method minimize endplate boneremoval on the whole, while still allowing for some removal along thevertebral endplate far lateral edges where the subchondral bone isthickest. Still further, certain embodiments of the interbody spinalimplant 1, 101, 101 a, 201, and 301 include smooth, rounded, and highlyradiused posterior portions and lateral sides which may minimizeextraneous bone removal for endplate preparation and reduce localizedstress concentrations. Thus, interbody surgical implant 1, 101, 101 a,201, and 301 and methods of using it are particularly useful inpreserving the natural arch of the vertebral endplate and minimizing thechance of implant subsidence.

Because the endplates are spared during the process of inserting thespinal implant 1, 101, 101 a, 201, and 301, hoop stress of the inferiorand superior endplates is maintained. Spared endplates allow thetransfer of axial stress to the apophasis. Endplate flexion allows thebone graft placed in the interior of the spinal implant 1 to accept andshare stress transmitted from the endplates. In addition, sparedendplates minimize the concern that BMP might erode the cancellous bone.

The interbody spinal implant 1 is durable and can be impacted betweenthe endplates with standard instrumentation. Therefore, certainembodiments of the invention may be used as the final distracter duringimplantation. In this manner, the disc space may be under-distracted(e.g., distracted to some height less than the height of the interbodyspinal implant 1) to facilitate press-fit implantation. Further, certainembodiments of the current invention having a smooth and roundedposterior portion (and lateral sides) may facilitate easier insertioninto the disc space. Still further, the surface roughened topography 80may lessen the risk of excessive bone removal during distraction ascompared to implants having teeth, ridges, or threads currently known inthe art even in view of a press-fit surgical distraction method.Nonetheless, once implanted, the interbody surgical implant 1 mayprovide secure seating and prove difficult to remove. Thus, certainembodiments of the interbody spinal implant 1, 101, 101 a, 201, and 301may maintain a position between the vertebral endplates due, at least inpart, to resultant annular tension attributable to press-fit surgicalimplantation and, post-operatively, improved osteointegration at one orboth of the top surfaces 81 of the integration plates 82.

Surgical implants and methods tension the vertebral annulus viadistraction. These embodiments and methods may also restore spinallordosis, thus improving sagittal and coronal alignment. Implant systemscurrently known in the art require additional instrumentation, such asdistraction plugs, to tension the annulus. These distraction plugsrequire further tertiary instrumentation, however, to maintain thelordotic correction during actual spinal implant insertion. If tertiaryinstrumentation is not used, then some amount of lordotic correction maybe lost upon distraction plug removal. Interbody spinal implant 1,according to certain embodiments of the invention, is particularlyadvantageous in improving spinal lordosis without the need for tertiaryinstrumentation, thus reducing the instrument load upon the surgeon.This reduced instrument load may further decrease the complexity, andrequired steps, of the implantation procedure.

Certain embodiments of the spinal implant 1, 101, 101 a, 201, and 301may also reduce deformities (such as isthmic spondylolythesis) caused bydistraction implant methods. Traditional implant systems requiresecondary or additional instrumentation to maintain the relativeposition of the vertebrae or distract collapsed disc spaces. Incontrast, interbody spinal implant 1, 101, 101 a, 201, and 301 may beused as the final distracter and thus maintain the relative position ofthe vertebrae without the need for secondary instrumentation.

Certain embodiments collectively comprise a family of implants, eachhaving a common design philosophy. These implants and the associatedsurgical techniques have been designed to address at least the ten,separate challenges associated with the current generation oftraditional anterior spinal fusion devices listed above in theBackground section of this document.

After desired annulotomy and discectomy, embodiments of the inventionfirst adequately distract the disc space by inserting (throughimpaction) and removing sequentially larger sizes of very smoothdistracters, which have been size matched with the size of the availableimplant 1. Once adequate distraction is achieved, the surgeon preparesthe end-plate with a rasp. There is no secondary instrumentationrequired to keep the disc space distracted while the implant 1, 101, 101a, 201, and 301 is inserted, as the implant 1, 101, 101 a, 201, and 301has sufficient mechanical strength that it is impacted into the discspace. In fact, the height of the implant 1, 101, 101 a, 201, and 301 ispreferably about 1 mm greater than the height of the rasp used forend-plate preparation, to create some additional tension in the annulusby implantation, which creates a stable implant construct in the discspace.

The implant geometry has features which allow it to be implanted via anyone of an anterior, antero-lateral, or lateral approach, providingtremendous intra-operative flexibility of options. The implant 1, 101,101 a, 201, and 301 has adequate strength to allow impact, and the sidesof the implant 1, 101, 101 a, 201, and 301 may have smooth surfaces toallow for easy implantation and, specifically, to prevent binding of theimplant 1, 101, 101 a, 201, and 301 to soft tissues during implantation.

The invention encompasses a number of different implant 1, 101, 101 a,201, and 301 configurations, including a composite implant formed of topand optional bottom plates (components), for example, made out oftitanium. The integration surfaces exposed to the vertebral body have aroughened surface topography 80 to allow for bony in-growth over time,and to provide resistance against expulsion. The top and bottom titaniumplates may be assembled together with the implant body. The net resultis a composite implant that has engineered stiffness for its clinicalapplication. The axial load may be borne by the polymeric component ofthe construct.

It is believed that an intact vertebral end-plate deflects like adiaphragm under axial compressive loads generated due to physiologicactivities. If a spinal fusion implant is inserted in the prepared discspace via a procedure which does not destroy the end-plates, and if theimplant contacts the end-plates only peripherally, the central dome ofthe end-plates can still deflect under physiologic loads. Thisdeflection of the dome can pressurize the bone graft material packedinside the spinal implant, hence allowing it to heal naturally. Theimplant 1, 101, 101 a, 201, and 301 designed according to certainembodiments allows the vertebral end-plate to deflect and allows healingof the bone graft into fusion.

Although illustrated and described above with reference to certainspecific embodiments and examples, the present invention is neverthelessnot intended to be limited to the details shown. Rather, variousmodifications may be made in the details within the scope and range ofequivalents of the claims and without departing from the spirit of theinvention. It is expressly intended, for example, that all rangesbroadly recited in this document include within their scope all narrowerranges which fall within the broader ranges. In addition, features ofone embodiment may be incorporated into another embodiment.

What is claimed is:
 1. A composite interbody spinal implant, comprising:a body having a top surface, a bottom surface, opposing lateral sides,opposing anterior and posterior portions, a substantially hollow center,and a single vertical aperture; an integration plate affixed to eitherthe top surface of the body or the bottom surface of the body, theintegration plate having a top surface, a bottom surface, opposinglateral sides, opposing anterior and posterior portions, and a singlevertical aperture extending from the top surface to the bottom surfaceof the integration plate and aligning with the single vertical apertureof the body, wherein the top surface of the integration plate has aroughened surface topography organized in a regular repeating patternincluding macro features, micro features, and nano features, withoutsharp teeth, and the roughened surface topography of the integrationplate generates implant migration-inhibiting friction between a vertebraand the integration plate when the implant is placed adjacent to thevertebra.
 2. The composite interbody spinal implant of claim 1, whereinthe roughened surface topography includes repeating micro features andnano features of smooth shapes oriented in opposition to a biologicforce on the implant.
 3. The composite interbody spinal implant of claim1, wherein the macro features, the micro features, and the nano featuresoverlap.
 4. The composite interbody spinal implant of claim 1, wherein:the macro features have a mean spacing between about 400-2,000 microns,a maximum peak-to-valley height between about 40-500 microns, and anaverage amplitude between about 20-200 microns; the micro features havea mean spacing between about 20-400 microns, a maximum peak-to-valleyheight between about 2-40 microns, and an average amplitude betweenabout 1-20 microns; and the nano features have a mean spacing betweenabout 0.5-20 microns, a maximum peak-to-valley height between about0.2-2 microns, and an average amplitude between about 0.01-1 microns. 5.The composite interbody spinal implant of claim 1, wherein the bodycomprises a non-metal.
 6. The composite interbody spinal implant ofclaim 5, wherein the non-metal is selected from the group consisting ofpolyetherether-ketone, and ultra-high molecular weight polyethylene. 7.The composite interbody spinal implant of claim 1, wherein theintegration plate comprises a metal.
 8. The composite interbody spinalimplant of claim 7, wherein the metal comprises titanium.
 9. Thecomposite interbody spinal implant of claim 1, wherein the singlevertical aperture (a) extends from the top surface to the bottomsurface, (b) has a size and shape predetermined to maximize the surfacearea of the top surface and the bottom surface available proximate theanterior and posterior portions while maximizing both radiographicvisualization and access to the substantially hollow center, and (c)optionally defines a transverse rim.
 10. The composite interbody implantof claim 1, wherein the roughened surface topography is further withoutsharp undercuts.
 11. A composite interbody spinal implant comprising: abody having a top surface, a bottom surface, opposing lateral sides,opposing anterior and posterior portions, a substantially hollow center,and a single vertical aperture; a first integration plate affixed to thetop surface of the body and a second integration plate affixed to thebottom surface of the body, wherein the first integration plate and thesecond integration plate each have a top surface, a bottom surface,opposing lateral sides, opposing anterior and posterior portions, and asingle vertical aperture extending from the top surface to the bottomsurface and aligning with the single vertical aperture of the body,wherein the top surface of the first integration plate and the topsurface of the second integration plate each have a roughened surfacetopography organized in a regular repeating pattern including macrofeatures, micro features, and nano features, without sharp teeth, andthe roughened surface topography of the first integration plategenerates implant migration-inhibiting friction between a first vertebraand the first integration plate, and the roughened surface topography ofthe second integration plate generates implant migration-inhibitingfriction between a second vertebra and the second integration plate whenthe implant is placed adjacent to the first vertebra and the secondvertebra.
 12. The composite interbody spinal implant of claim 11,wherein the first integration plate and the second integration platecomprise a metal and the body comprises a non-metal.
 13. The compositeinterbody implant of claim 12, wherein the metal comprises titanium. 14.The composite interbody implant of claim 12, wherein the non-metalcomprises a polymer.
 15. The composite interbody implant of claim 12,wherein the non-metal is selected from the group consisting ofpolyetherether-ketone, and ultra-high molecular weight polyethylene. 16.The composite interbody implant of claim 11, wherein the roughenedsurface topographies of the first integration plate and the secondintegration plate include repeating micro features and nano features ofsmooth shapes oriented in opposition to a biologic force on the implant.17. The composite interbody spinal implant of claim 11, wherein themacro features, the micro features, and the nano features of theroughened surface topographies of the first integration plate and thesecond integration plate overlap.
 18. The composite interbody spinalimplant of claim 11, wherein: the macro features of the roughenedsurface topographies of the first integration plate and the secondintegration plate have a mean spacing between about 400-2,000 microns, amaximum peak-to-valley height between about 40-500 microns, and anaverage amplitude between about 20-200 microns; the micro features ofthe roughened surface topographies of the first integration plate andthe second integration plate have a mean spacing between about 20-400microns, a maximum peak-to-valley height between about 2-40 microns, andan average amplitude between about 1-20 microns; and the nano featuresof the roughened surface topographies of the first integration plate andthe second integration plate have a mean spacing between about 0.5-20microns, a maximum peak-to-valley height between about 0.2-2 microns,and an average amplitude between about 0.01-1 microns.
 19. The compositeinterbody implant of claim 11, wherein the roughened surface topographyof the top surface of the first integration plate and the roughenedsurface topography of the top surface of the second integration plateare further without sharp undercuts.